Method and article for concentrating fields at sense layers

ABSTRACT

A write line structure for a magnetic memory cell includes a write conductor having a front surface facing the memory cell, a back surface and two sides surfaces. A cladding layer is disposed adjacent a portion of the front surface of the write conductor, with the cladding layer terminating at spaced first and second poles adjacent the front surface of the write conductor. A data storage layer is operatively positioned adjacent the cladding layer. The distance between the poles is less than the width of the write conductor. The width of the data storage layer may be greater than or less than the distance between the poles.

THE FIELD OF THE INVENTION

[0001] The present invention generally relates to magnetic random accessmemory (MRAM) devices. More particularly, the present invention relatesto ferromagnetic cladding for concentrating a magnetic field at a senselayer.

BACKGROUND OF THE INVENTION

[0002] An MRAM device includes an array of memory cells. The typicalmagnetic memory cell includes a layer of magnetic film in which themagnetization is alterable and a layer of magnetic film in which themagnetization is fixed or “pinned” in a particular direction. Themagnetic film having alterable magnetization may be referred to as adata storage layer or sense layer and the magnetic film which is pinnedmay be referred to as a reference layer.

[0003] Conductive traces (commonly referred to as word lines and bitlines) are routed across the array of memory cells. Word lines extendalong rows of memory cells, and bit lines extend along columns of memorycells. Because the word lines and bit lines operate in combination toswitch the orientation of magnetization of the selected memory cell(i.e., to write the memory cell) the word lines and bit lines can becollectively referred to as write lines. Additionally, the write linescan also be used to read the logic values stored in the memory cell.

[0004] Located at each intersection of a word line and a bit line is amemory cell. Each memory cell stores a bit information as an orientationof a magnetization. Typically, the orientation of magnetization in thedata storage layer aligns along an axis of the data storage layer thatis commonly referred to as its easy axis. External magnetic fields areapplied to flip the orientation of magnetization in the data storagelayer along its easy axis to either a parallel or anti-parallelorientation with respect to the orientation of magnetization in thereference layer, depending on the desired logic state (i.e., “1” or“0”).

[0005] The orientation of magnetization of each memory cell will assumeone of two stable orientations at any given time. These two stableorientations are referred to as parallel and anti-parallel, andrepresent logic values of “1” and “0”. The orientation of magnetizationof a selected memory cell may be changed by supplying current to a wordline and a bit line which intersect at the selected memory cell. Thecurrents create magnetic fields that, when combined, can switch theorientation of magnetization of the selected memory cell from parallelto anti-parallel or vice versa.

[0006] A selected magnetic memory cell is usually written by applyingelectrical currents to the particular word and bit lines that intersectthe selected magnetic memory cell. An electrical current applied to theparticular bit line generates a magnetic field substantially alignedalong the easy axis of the selected magnetic memory cell. The magneticfield aligned to the easy axis may be referred to as a longitudinalwrite field. An electrical current applied to the particular word lineusually generates a magnetic field substantially perpendicular to theeasy axis of the selected magnetic memory cell.

[0007] Preferably, only the selected magnetic memory cell receives boththe longitudinal and the perpendicular write fields. Other memory cellscoupled to the particular word line preferably receive only theperpendicular write field. Other magnetic memory cells coupled to thebit line preferably receive only the longitudinal write field.

[0008] The magnitudes of the longitudinal and perpendicular write fieldsare usually selected to be high enough so that the chosen magneticmemory cell switches its logic state when subjected to both longitudinaland perpendicular fields, but low enough so that the other magneticmemory cells which are subject only to either the longitudinal or theperpendicular write fields do not switch. The undesirable switching of amagnetic memory cell that receives only the longitudinal or theperpendicular right field is commonly referred to as “halfselect”switching.

[0009] Manufacturing variation among the magnetic memory cells oftenincrease the likelihood of half-select switching. For example,manufacturing variations in the longitudinal or perpendicular dimensionsor shapes of the memory cells may increase the likelihood of half-selectswitching. In addition, variation in thickness or the crystallineanisotropy of the data storage layers may increase the likelihood ofhalf-select switching. Unfortunately, such manufacturing variationsdecrease the yield of manufacturing processes for magnetic memories andreduce the reliability of magnetic memories.

[0010] As with nearly every electronic device, it is desirable to reducethe size and increase the package density of MRAM devices. However, anumber of factors influence the package density that can be achieved foran MRAM device. First, the size of the memory cells usually mustdecrease with increasing package densities. Unfortunately, reducing thesize of the memory cell can result in an increase of the magnetic fieldthat is required to switch the magnetic orientation of the memory cell.

[0011] A second factor influencing the package density of an MRAM deviceis the size of the write lines themselves. As with the memory cells, thedimensions of the write lines must typically decrease with increasedpackage density. However, reducing the dimensions of the write linesresults in a corresponding reduction in the current that can be carriedby the write lines. A reduction in current carried by the write linesresults in a weaker magnetic field at the selected memory cell andimpedes the ability to write the memory cell.

[0012] A third factor which influences the package density of an MRAMdevice is the distance between a write line and an adjacent memory cell(e.g., a memory cell that is not the “selected” memory cell between theintersecting word and bit lines). As the distance between the writelines and adjacent memory cells decreases, the possibility increasesthat the magnetic field produced by a write line may inadvertently andadversely affect the information stored in an adjacent memory cell.

[0013] The problems associated with increasing the package density of anMRAM device have been addressed by others. For example, U.S. Pat. No.5,039,655 to Pisharody discloses the use of a superconducting materialaround the three sides of a write line that are not adjacent to a memorycell. The superconducting material effectively shunts the magnetic fieldcreated by the current in the write line and directs the magnetic fieldtoward the magnetic storage material of the memory cell. Similarly, U.S.Pat. No. 5,956,267 to Hurst et al., discloses a word line structure andmethod of manufacture therefore which improves upon the structure andconstruction methods of Pisharody.

[0014] One limitation of Pisharody and Hurst et al. is that the fluxconcentration means taught therein are restricted to three of the foursides of the write conductor. The maximum write field for a given writecurrent is thereby limited by the width of the write conductor. A writeline construction that overcomes this limitation and permits thecreation of a stronger magnetic write field for a given write line widthand/or a given current would be desirable.

[0015] Another limitation of Pisharody and Hurst et al. is that the fluxconcentration means which are formed around the write lines permit thecreation of both a longitudinal component of magnetic field in the senselayer of the memory cell, as well as a perpendicular component of themagnetic field. The perpendicular component of the magnetic field is atbest wasted in that it is unable to contribute to the orientation of thesense layer of the memory cell, and is perhaps harmful in that theperpendicular field may adversely affect adjacent memory cells. Thus, itwould be desirable in some instances to provide a write line structurein which the longitudinal field components are reinforced and theperpendicular field components are reduced or eliminated entirely.

SUMMARY OF THE INVENTION

[0016] The present invention provides a cladded write conductor for usein a magnetic random access memory device. The cladded write conductorof the present invention permits the creation of a stronger magneticwrite field for a given write line width and/or a given current.

[0017] In one embodiment, the write line structure for a magnetic memorycell comprises a write conductor having a front surface facing thememory cell, a back surface and two sides surfaces. A cladding layer isdisposed adjacent a portion of the front surface of the write conductor,with the cladding layer terminating at spaced first and second polesadjacent the front surface of the write conductor. A data storage layeris operatively positioned adjacent the cladding layer. The distancebetween the poles is less than the width of the write conductor. Thewidth of the data storage layer may be greater than or less than thedistance between the poles.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1a is a schematic representation of a prior art magneticfield keeper.

[0019]FIG. 1b is a greatly enlarged portion of the prior art magneticfield keeper of FIG. 1a illustrating the components of the magneticfield in the sense layer.

[0020]FIG. 2a is a schematic representation of an embodiment of thecladded write conductor of the present invention.

[0021]FIG. 2b is a greatly enlarged portion of the cladded writeconductor of FIG. 2a illustrating the components of the magnetic fieldin the sense layer.

[0022]FIG. 3a is a schematic representation of another embodiment of thecladded write conductor of the present invention.

[0023]FIG. 3b is a greatly enlarged portion of the cladded writeconductor of FIG. 3a illustrating the components of the magnetic fieldin the sense layer.

[0024]FIG. 4 is a perspective view of an MRAM device using the presentinvention.

[0025]FIGS. 5a and 5 b illustrate alternate sense layer shapes.

[0026]FIGS. 6a-6 d illustrate possible pole designs for the presentinvention.

[0027]FIGS. 7a-7 g illustrate a process for forming one embodiment ofthe cladded write conductor of the present invention.

[0028]FIG. 8 illustrates an alternate process step for forming adifferent construction of the cladded write conductor of the presentinvention.

[0029]FIG. 9 illustrates a memory cell traversing a cladded writeconductor having non-planarized pole extensions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] In the following detailed description of the preferredembodiments, reference is made to the accompanying drawings which form apart hereof, and in which is shown by way of illustration specificembodiments in which the invention may be practiced. It is to beunderstood that other embodiments may be utilized and structural orlogical changes may be made without departing from the scope of thepresent invention. The following detailed description, therefore, is notto be taken in a limiting sense, and the scope of the present inventionis defined by the appended claims.

[0031] In FIG. 1a, a prior art write line structure 10 is schematicallyrepresented. Magnetic field keeper 11 is positioned such that write line12 is covered on its back surface 14 and side surfaces 16 by magneticfield keeper 11. The poles 18 of magnetic field keeper 11 areapproximately flush with the front surface 20 of write line 12 andseparated by a distance D_(P0). Sense layer 22 of the magnetic memorycell is positioned adjacent the front surface 20 of write line 12, suchthat sense layer 22 of the memory cell is positioned above and betweenpoles 18 of magnetic field keeper 11.

[0032] The portion of FIG. 1a enclosed by dashed circle 30 is showngreatly enlarged in FIG. 1b. The magnetic field emanating from poles 18of magnetic field keeper 11 is represented by vector 32. As illustrated,magnetic field vector 32 includes both a longitudinal component 34 and aperpendicular component 36. The longitudinal component 34 is directedalong the easy axis of the sense layer 22 and contributes to theswitching of the magnetization in the sense layer 22. Because thestrength of the magnetic write field is inversely proportional to thedistance D_(P0) between poles 18, for a given current the strength ofthe write field is limited by the width of the write line 12. The priorart structure 10 is thus limited in its ability to compensate foreverdecreasing memory cell sizes and the need for a stronger write fieldfrom the word lines.

[0033] The present invention utilizes a novel cladding structure aboutthe write line conductors to decrease the distance between the poles ofthe flux concentration means, and thereby produce a greater write fieldfor a given current and write line width. The present invention is notlimited by the width of the write line, as in the prior art.

[0034]FIG. 2a shows one embodiment of the present invention in which awrite conductor 40 having a width W_(C1) is surrounded by cladding 42 onits back surface 44, side surfaces 46, and a portion of its frontsurface 48. Cladding 42 terminates at poles 50 which are positionedalong front surface 48 and away from side surfaces 46. Poles 50 arespaced from each other by a distance D_(P1) which is less than W_(C1).The sense layer 52 of the magnetic memory cell has a width W_(S1) whichis less than D_(P1) and is positioned directly between poles 50. Asdiscussed below with respect to FIGS. 3a and 3 b, the sense layer 52 mayalso have a width greater than D_(P1).

[0035] The portion of FIG. 2a enclosed by circle 60 is shown in FIG. 2b.The magnetic field emanating from poles 50 of cladding 42 is representedby vector 62. As illustrated, magnetic field vector 62 has only alongitudinal component and no perpendicular component. Thus, in theembodiment of FIGS. 2a and 2 b the entire magnetic field generated bywrite conductor 40 is utilized to switch the orientation ofmagnetization of sense layer 52.

[0036] The construction as shown in FIGS. 2a and 2 b provides multipleadvantages over the prior art. First, poles 50 are positioned closer toeach other than allowed by prior art devices. That is, D_(P1) is lessthan W_(C1). This allows a stronger write field to be created for agiven current and write line width. Second, because sense layer 52 ispositioned directly between poles 50, there is no significantperpendicular component of the magnetic field. Rather, the entiremagnetic field is directed in the longitudinal direction. Thus, astronger magnetic field may be formed in the sense layer 52 for a givencurrent in write line 40. Alternately, a lower current may be providedin write line 40 for a desired magnetic field strength.

[0037]FIG. 3a shows another embodiment of the present invention in whicha write conductor 70 having a width W_(C2) is surrounded by cladding 72on its back surface 74, side surfaces 76, and a portion of its frontsurface 78. Cladding 72 terminates at poles 80 which are positionedadjacent to the front surface 78 and away from the side surfaces 76.Poles 80 are spaced from each other by a distance D_(P2) which is lessthan the width W_(C2) of the conductor 70. This confers the advantagethat the poles 80 are positioned closer to each other than allowed byprior art devices (i.e., the distance between poles 80 is less than thewidth of the write line 70), thereby allowing a stronger write field tobe created for a given current and write line width. In this embodiment,a sense layer 82 having a width W_(S2) is positioned above the poles 80,such that poles 80 are positioned between front surface 78 and senselayer 82. Width W_(S2) of sense layer 82 is greater than the spacingD_(P2) between poles 80, which is important for reasons elaborated uponbelow.

[0038] The portion of FIG. 3a enclosed by circle 90 is shown greatlyenlarged in FIG. 3b. The magnetic field emanating from poles 80 ofcladding 72 is represented by vector 92. The magnetic field vector 92has both a longitudinal component 94 and a perpendicular component 96,as in the prior art devices discussed above. However, the constructionof FIGS. 3a and 3 b has the advantage over the prior art devices in thata higher magnitude magnetic field will be created in a narrower regionof sense layer 82. That is, the construction shown in FIGS. 3a and 3 bmimics the effect of write conductor 70 being narrower than sense layer82, without W_(C2) actually being less than W_(S2).

[0039] The benefits of write conductors being smaller in dimension thanthe sense layer of the memory cell are described in U.S. Pat. No.6,236,590 to Bhattacharyya et al., which is herein incorporated byreference. Specifically, the advantages of the write conductors havingdimensions smaller than the dimensions of the sense layer include butare not limited to: improved coupling of a write magnetic field with thesense layer so that the write magnetic field is not wasted or reduceddue to misalignments between the sense layer and the write conductor;reduced possibility of misalignments between the write conductors andthe sense layers; elimination or reduction of leakage magnetic fieldsthat may interfere with adjacent memory cells; an increase in themagnitude of the magnetic field for a given current; and the ability togenerate a magnetic field necessary to rotate the orientation ofmagnetization of the sense layer with a reduced magnitude of current,thereby reducing power consumption by the MRAM device.

[0040] The embodiment of the invention shown in FIGS. 3a and 3 bprovides all of the advantages enumerated above, without requiring anactual reduction in size of the write conductor. The ability to mimicthe effects of the write conductor being narrower than the sense layer,without actually reducing the dimensions of the write conductor orincreasing the size of the sense layer, is advantageous for severalreasons. First, manufacturing write conductors of ever decreasing sizebecomes increasingly difficult and expensive. Second, decreasing thesize of the write conductors may introduce undesirable consequenceswhich the offset the benefits of the write conductors being smaller indimension than the sense layers. Specifically, reducing the dimensionsof the write conductor results in a corresponding increase in resistanceof the conductor. The increased resistance of the write conductorintroduces the need for a higher voltage source to drive the currentthrough the write conductor. Also, a higher resistance in the writeconductor increases the amount of heat generated by the MRAM device,which may prove difficult to dissipate. Decreasing the area of the writeconductor also increases the current density in the write conductor,which may lead to undesirable electromigration.

[0041] Although the examples of the present invention as shown in FIGS.2a, 2 b, 3 a and 3 b illustrate only a single write conductor (that is,only the word line or the bit line), it will readily be recognized bythose skilled in the art that the principles discussed above mayadvantageously be used with both word lines and bit lines in a magneticrandom access memory, either in combination or alone. As shown in FIG.4, a magnetic memory cell 100 having a data storage layer 101 ispositioned between a first conductor 102 and a second conductor 104. Thefirst conductor 102 has a width W_(C3) and extends in a first direction106, and the second conductor 104 has a width W_(C4) and extends in asecond direction 108. In a preferred embodiment, the first and seconddirections 106, 108 are generally orthogonal to each other. However, theinvention described herein is equally applicable when the first andsecond directions 106, 108 are not orthogonal. The data storage layer101 has a first layer width W_(S3) in the first direction 106, and asecond layer width W_(S4) in the second direction 108. The data storagelayer 101 has an easy axis which is generally aligned with the seconddirection 108. It will be noted that in FIG. 4, data storage layer 101and cladding 110 are positioned about first and second conductors 102,104 as exemplified above in FIGS. 3a and 3 b. However, data storagelayer 101 and cladding 110 may alternately be configured as describedabove with respect to FIGS. 2a and 2 b.

[0042] In all of the examples given above, cladding 42, 72, 110preferably is comprised of high permeability ferromagnetic materials.Examples of preferred cladding material alloys are NiFe, CoFe, Co, Fe,FeN, and amorphous Co-based alloys (CoZrNb, CoTaNb, CoHfNb). Thoseskilled in the art will recognize that other materials may also besuitable for the purposes intended. The cladding materials forming thepole extensions on the front surface of the write conductors need not bethe same as the cladding materials on the other three sides of theconductor. The thickness of the cladding layers is preferably in therange of 1 to 50 nm, and more preferably in the range of 5-15 nm.

[0043] The sense layers 52, 82, 101 described above can bemagnetoelectric devices that include but are not limited to spindependent tunneling devices, spin valve devices, and giantmagnetoresistive devices. Further, although the sense layers 52, 82, 101are illustrated heretofore as having rectangular shapes, the senselayers 52, 82, 101 may have shapes that include but are not limited to arectangular shape, a polygon shape 101 ′, and an arcuate shape 101 ″, asillustrated in FIGS. 5a and 5 b, respectively.

[0044] The design of the poles 50, 80 may be selected so as to maximizethe magnetic field for a given current. Examples of preferred poledesigns are shown in FIGS. 6a-6 d, by way of the example only. Each ofthe illustrated pole designs act to sharpen the edge of the poles so asto more highly concentrated the magnetic field emanating from the poles.Those skilled in the art will recognize a multitude of additional poleshapes which will also serve for the intended purpose.

[0045] The embodiments described in this invention may be fabricated bythose skilled in the art using known methods of deposition, lithography,etch and planarization common to semiconductor manufacturing.

[0046] It is recognized that one implementation of this invention mayrequire patterned features with lateral dimensions less than the minimumfeature size k allowed by the lithography system. Referring to FIG. 3a,for example, the distance D_(P2) may be less than λ. A process forgenerating the gap between the poles of the cladding at sub-λ dimensionsis described below with reference to FIGS. 7a-7 g.

[0047] First, an assembly of planarized conductors 120 having cladding122 is fabricated within a matrix of dielectric 124, as shown in FIG.7a. Damascene processing may be employed to create such conductors.Cladding 122 preferably includes a layer of ferromagnetic material, andmay also include a barrier layer between the layer of ferromagneticmaterial and the conductor 120. Next, a layer of ferromagnetic material126 that will serve as pole extensions is deposited, followed by adielectric layer 128. Photolithographic and etch processes are used toremove both the dielectric and ferromagnetic layers 128, 126,respectively, in regions 130 (defined by photoresist 129) between thecladded conductors 120, as shown in FIG. 7b. A second dielectric layer132 is deposited over the patterned films, and the two dielectric layers128, 132 are then planarized to form the structure of FIG. 7c.Preferential etching of the first dielectric 128 leaves the seconddielectric 132 between the conductors 120. Conformal deposition of athird dielectric 134 creates the topography illustrated in FIG. 7d.Exposing this structure to a highly anisotropic etch removes dielectriconly in the vertical dimension, allowing a narrow via 136 to be formeddown to the ferromagnetic material 126. At this point the ferromagneticmaterial 126 is etched to create the pole extensions 138 and gap D_(P)between the poles 140, which can be less than λ (refer to FIG. 7e).

[0048] If a planarized surface is desired, a fourth dielectric layer 142is deposited to fill the via 136 regions (FIG. 7f) and then planarized(FIG. 7g). Alternatively, the dielectric films remaining after step 7 ecan be etched to create the cladded conductors of FIG. 8. Traditionaldeposition and patterning methods can then be employed to create thememory cell on top of these structures.

[0049] Referring to FIG. 3A, the magnetic sense layer 82 in the memorycell can be either in direct contact with the pole extensions 81, orphysically separated from the pole extensions by an intervening layer.Additionally, it is not a requirement that the pole extensions 81 beplanarized, as indicated in FIG. 7g, prior to deposition of the memorycell or sense layer.

[0050] The thickness of the pole extensions may be as little as 1 nm, ispreferably on the order of 1 to 50 nm, and more preferably on the orderof 5 to 15 nm. A memory cell 142 traversing non-planarized poleextensions 138 is shown in FIG. 9. It is also noted that neither thememory cell 142 (including the sense layer) nor the gap D_(P) betweenthe pole extensions 138 have to be centered above the conductormaterial.

[0051] Although specific embodiments have been illustrated and describedherein for purposes of description of the preferred embodiment, it willbe appreciated by those of ordinary skill in the art that a wide varietyof alternate and/or equivalent implementations may be substituted forthe specific embodiments shown and described without departing from thescope of the present invention. Those with skill in theelectromechanical and electrical arts will readily appreciate that thepresent invention may be implemented in a very wide variety ofembodiments. This application is intended to cover any adaptations orvariations of the preferred embodiments discussed herein. Therefore, itis manifestly intended that this invention be limited only by the claimsand the equivalents thereof.

What is claimed is:
 1. A write line structure for a magnetic memory device having a magnetic field sensitive memory cell, comprising: a write conductor having a front surface adjacent the memory cell, a back surface and two sides surfaces; a cladding layer adjacent the back surface, the two sides surfaces and a portion of the front surface of the write conductor, the cladding layer including a layer of magnetic material.
 2. The write line structure of claim 1, further comprising a barrier layer between the write conductor and the layer of magnetic material.
 3. The write line structure of claim 1, wherein the cladding layer adjacent the front surface of the write conductor forms two pole pieces adjacent to the front surface of the write conductor.
 4. The write line structure of claim 3, wherein the pole pieces of the cladding layer are spaced from each other by a distance less than a width of the front surface of the write conductor.
 5. The write line structure of claim 3, wherein the magnetic memory cell is positioned between the pole pieces adjacent the front surface of the write conductor.
 6. The write line structure of claim 3, wherein the pole pieces are positioned between the front surface of the write conductor and the magnetic memory cell.
 7. The write line structure of claim 6, wherein the magnetic memory cell has a width greater than the spacing between the pole pieces.
 8. The write line structure of claim 7, wherein the magnetic memory cell is spaced from the pole pieces.
 9. The write line structure of claim 7, wherein the magnetic memory cell is in contact with the pole pieces.
 10. The write line structure of claim 1, wherein the cladding layer has a thickness in the range of 1 to 50 nm.
 11. The write line structure of claim 1, wherein the cladding layer has a thickness in the range of 5 to 15 nm.
 12. The write line structure of claim 1, wherein the magnetic material is selected from the group consisting of NiFe, CoFe, Co, Fe, FeN, CoZrNb, CoTaNb, and CoHfNb.
 13. The write line structure of claim 1, wherein the memory cell is a spin dependant tunneling device.
 14. The write line structure of claim 1, wherein the memory cell is a spin valve device.
 15. The write line structure of claim 1, wherein the memory cell is a giant magnetoresistive device.
 16. A write line structure for a magnetic memory cell, comprising: a write conductor having a front surface facing the memory cell, a back surface and two sides surfaces, the write conductor having a first width; a cladding layer disposed adjacent a portion of the front surface of the write conductor, the cladding layer terminating at first and second poles adjacent the front surface of the write conductor, the first and second polls separated from each other by a second width; and a data storage layer operatively positioned adjacent the cladding layer, the data storage layer having a third width; wherein the second width is less than the first width.
 17. The write line structure of claim 16, wherein the second width is greater than the third width.
 18. The write line structure of claim 16, wherein the second width is less than the third width.
 19. The write line structure of claim 16, wherein the cladding layer includes a layer of magnetic material.
 20. The write line structure of claim 16, wherein the cladding layer is further disposed adjacent the back surface and two sides surfaces of the write conductor.
 21. The write line structure of claim 16, wherein the poles are tapered.
 22. A write conductor layout structure for a magnetic memory cell, comprising: a first conductor having a first width; a second conductor having a second width; a data storage layer operatively positioned between the first conductor and the second conductor and having a first layer width in a first direction and a second layer width in a second direction, the first and second conductors crossing the data storage layer in substantially the first and second directions, respectively; a first cladding layer disposed about the first conductor and terminating at a first set of poles between the first conductor and the data storage layer, the first set of poles separated by a first spacing; and a second cladding layer disposed about the second conductor and terminating at a second set of poles between the second conductor and the data storage layer, the second set of poles separated by a second spacing; wherein the first spacing between the first set of poles is less than the first width of the first conductor and is less than the second layer width of the data storage layer.
 23. The write conductor layout structure of claim 22, wherein the second spacing between the second set of poles is less than the second width of the second conductor and is less than the first layer width of the data storage layer.
 24. The write conductor layout structure of claim 22, wherein a selected one of the first direction or the second direction is co-linear with an easy axis of the data storage layer.
 25. The write conductor layout structure of claim 22, wherein the data storage layer is a magnetoelectric device selected from the group consisting of a spin dependent tunneling device, a spin valve device, and a giant magnetoresistive device.
 26. The write conductor layout structure of claim 22, wherein the first and second directions are substantially orthogonal to each other such that the first conductor and the second conductor cross the data storage layer in substantially orthogonal relation to each other.
 27. A method for concentrating a magnetic field in a sense layer of a magnetic memory cell, comprising: forming a cladding layer on a write conductor having a front surface, a back surface and two sides surfaces, the cladding including a layer of magnetic material disposed adjacent the back, side and front surfaces of the write conductor, the cladding layer terminating at first and second poles adjacent the front surface of the write conductor; and placing a data storage layer adjacent the first and second poles of the cladding.
 28. The method of claim 27, wherein the data storage layer is positioned between the first and second poles.
 29. The method of claim 27, wherein the first and second poles are positioned between the front surface of the write conductor and the data storage layer.
 30. The method of claim 29, wherein the poles are separated from each other by a distance less than a width of the data storage layer.
 31. A method for forming a write line structure for a magnetic memory device, the method comprising the steps of: fabricating an assembly of cladded conductors within a matrix of dielectric material, the conductors having ferromagnetic cladding on a bottom surface and two side surfaces of the conductors; planarizing an upper surface of the assembly of cladded conductors; depositing a layer of ferromagnetic material on the planarized upper surface of the assembly of conductors; depositing a layer of a first dielectric material over the layer of ferromagnetic material; patterning the ferromagnetic material and first dielectric material by removing the ferromagnetic material and first dielectric material between the cladded conductors; depositing a layer of a second dielectric material over the patterned ferromagnetic material and first dielectric material; planarizing the layers of the first and second dielectric materials; patterning the first and second dielectric materials by preferentially etching the first dielectric material to leave only the second dielectric material between the cladded conductors; depositing a layer of a third dielectric material over the patterned second dielectric material; forming a via through the third dielectric material and ferromagnetic material to each of the conductors in the assembly, thereby leaving ferromagnetic pole extensions over the upper surface of the cladded conductors;
 32. The method for forming a write line structure for a magnetic memory device of claim 31, wherein the step of fabricating an assembly of cladded conductors employs damascene processing.
 33. The method for forming a write line structure for a magnetic memory device of claim 31, wherein photolithographic and etch processes are used to remove the ferromagnetic material and first dielectric material between the cladded conductors.
 34. The method for forming a write line structure for a magnetic memory device of claim 31, wherein the step of forming a vias comprises a highly anisotropic etch to remove the third and second dielectric materials only in the vertical dimension.
 35. The method for forming a write line structure for a magnetic memory device of claim 31, wherein the via is formed with a width which is less than a minimum feature size of a lithography process used to form the write line structure.
 36. The method for forming a write line structure for a magnetic memory device of claim 31, further comprising the steps of: depositing a layer of a fourth dielectric material to fill the vias; and planarizing the pole extensions, second dielectric material and fourth dielectric material.
 37. The method for forming a write line structure for a magnetic memory device of claim 31, further comprising the steps of: removing the remaining dielectric remaining materials.
 38. The method for forming a write line structure for a magnetic memory device of claim 37, wherein the remaining dielectric materials are removed by etching.
 39. The method for forming a write line structure for a magnetic memory device of claim 36, further comprising the steps of: forming a magnetic memory cell over the cladded conductors.
 40. The method for forming a write line structure for a magnetic memory device of claim 39, wherein the memory cell has a magnetic sense layer in direct contact with the pole extensions.
 41. The method for forming a write line structure for a magnetic memory device of claim 39, wherein the memory cell has a magnetic sense layer physically separated from the pole extensions by an intervening layer.
 42. The method for forming a write line structure for a magnetic memory device of claim 37, further comprising the steps of: forming a magnetic memory cell over the cladded conductors.
 43. The method for forming a write line structure for a magnetic memory device of claim 42, wherein the memory cell has a magnetic sense layer in direct contact with the pole extensions.
 44. The method for forming a write line structure for a magnetic memory device of claim 42, wherein the memory cell has a magnetic sense layer physically separated from the pole extensions by an intervening layer.
 45. The method for forming a write line structure for a magnetic memory device of claim 31, wherein the thickness of the ferromagnetic material on the upper surface is in the range of 1 to 50 nm. 